Abstract

Carbon fibre-reinforced plastic (CFRP) is an often-used structural material in the high-tech industries, like aerospace, wind turbine, sport, automobile, robotics and military. Due to both the growing application area of composites, and the advanced construction requirements, the used thickness of the CFRP plates increases, and the necessity of drilling holes on the sides of the plates (normal II direction) becomes even more important. Many researchers studied the machinability of UD-CFRP using numerous drilling experiments at the normal I direction. However, drilling experiments at normal II and axial directions were not published yet. The main objective of the present study is to analyse and discuss the influence of a non-conventional drilling direction on hole-quality parameters and on the thrust force. Drilling experiments were carried out in unidirectional CFRP at non-conventional drilling direction, based on central composite inscribed design. Influences of feed rate and cutting speed were analysed using response surface methodology (RSM) and analysis of variance (ANOVA) techniques. Characteristics of uncut fibres were analysed using digital image processing (DIP). The results have proved that the effect of the cutting speed is more significant when drilling UD-CFRP at the non-conventional drilling direction than at the conventional one. Furthermore, the specific feed force (kf) in the case of the non-conventional drilling direction was more than three times higher than the kf in the case of the conventional one.

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Acknowledgements

Furthermore, the authors acknowledge Prof. Gyula MÁTYÁSI, Norbert FORINTOS and András TŐKE for their participation in the experimental work.

Funding information

The authors was provided support by the CEEPUS III HR 0108 project. This research was partly supported by the EU H2020-WIDESPREAD-01-2016-2017-TeamingPhase2-739592 project “Centre of Excellence in Production Informatics and Control” (EPIC). This work was partly supported by the Higher Education Excellence Program of the Ministry of Human Capacities in the frame of Nanotechnology and Material Science research area of Budapest University of Technology and Economics (BME FIKP-NANO).